A problem in a number of consumer products is that digital content must be transmitted along signal paths that can be tapped into. As a result, digital content providers are concerned about unauthorized copying of digital content by hackers. For example, a home entertainment system may include a personal computer (PC), graphics sub-system, high-definition television, set-top boxes, digital video recorders and players, and digital versatile disk (DVD) players. Consequently, there is a risk that unencrypted digital content (often known as “clear text” content) may be intercepted by a hacker using, for example, the output of one or more signal buses.
Digital content protection is of increasing importance to protect audio and video content from unauthorized copying. Digital content protection includes, among other things, protocols for encrypting content that will be transmitted over signal buses that can be tapped into. A digital transmission content protection (DTCP) scheme was developed in 1998 by five companies (5C) and is described in the white paper, “5C Digital Transmission Content Protection,” published July 1998 by Hitachi, Ltd. Intel Corporation, Matsushita Electric Industrial, Co., Sony Corporation, and Toshiba Corporation, the contents of which are hereby incorporated by reference. Additional details of the DTCP method are described in the “Digital Transmission Content Protection Specification,” revision 1.3, published January 2004 by Hitachi, Ltd. Intel Corporation, Matsushita Electric Industrial, Co., Sony Corporation, and Toshiba Corporation, the contents of which are hereby incorporated by reference. The DTCP method may be used with an Institute of Electrical and Electronics Engineers (IEEE) 1394 multimedia bus and includes a protocol for a source device and a sink device (a device that can receive a stream of content) to establish secure transmission of content. The DTCP method includes an authentication and key exchange (AKE) protocol, content encryption, and copy control information (CCI) using an encryption mode indicator (EMI).
One drawback of digital content protection schemes, such as DTCP, is that although content is encrypted on inter-device system buses, clear text data is susceptible to theft at one or more internal data buses. For example, consider DVD playback in a PC based multimedia system. DVD content is received from a DVD player in an encrypted form by a central processing unit (CPU). The CPU decrypts the digital content that it receives. The CPU then re-encrypts the DVD data before writing the data to a display device. However, the decryption and re-encryption performed by the CPU typically necessitates that clear-text data is written to a system memory, where the content is susceptible to theft at a memory bus.
Another drawback of digital content protection schemes is that they impose a significant burden on a CPU performing encryption and decryption of high definition video. For example, the Advanced Encryption Standard (AES) imposes an approximately 16 cycles/Byte (B) encryption cost. Compressed format high definition television (HDTV) corresponds to about 50 MB/s encryption bandwidth such that each high-resolution compressed HDTV content stream corresponds to 800 MHz of the available CPU clock cycles. This is a significant burden on a CPU operating a clock rate of a few Gigahertz. Moreover, in some multimedia systems it is desirable to have the capability to simultaneously handle several video streams such that in the worst case scenario the total encryption/decryption burden on a CPU can consume the majority of CPU clock cycles.
Therefore what is desired is an improved system and method for providing digital content protection.